Conventional motorcycle frames use steel tubing welded into closed frameworks to interconnect various components (e.g., front assembly, seat, engine, etc.) and transmit the loads therebetween. The metal tubes keep the components in a substantially fixed spatial relation, i.e., they maintain the components relative proximity. Moreover, the metal tubes bear the in-plane and out-of-plane loads between the components.
Traditionally, metal motorcycle frames have a top tube that is connected at its front end to a relatively short head tube. Normally, the top tube extends generally horizontally backward under the gas tank and then under the seat. Typically, the top tube bifurcates under the seat into two tubes, which are each connected to a generally vertical rear support tubes. A pair of down tubes is usually connected at their front ends to the head tube and extend downwardly and then rearwardly under the engine, connecting at their ends to the rear support tubes. The vertical rear support tubes can be movably connected to a swing arm that supports the rear wheel in what is known in the art as a “soft tail” frame or can be fixedly connected at its top and bottom ends to tubes that converge together and support the rear wheel in what is known as a “hard tail” frame.
Such metal tube frames are relatively heavy, since they are typically formed from the extrusion or rolling and seaming of steel or other metal alloys. Moreover, conventional tube frames are limited in terms of aerodynamic improvements, as they are restricted to the use of tubes of generally circular cross-sections.
The strength of conventional metal frames can be compromised due to several factors. For example, the joints between each respective tube (e.g., for example, the connection between the head tube and top tube) are points of stress. Thus, any weakness in the joint will reduce the strength of the frame. Further, metal traditionally does not have a high flex modulus such that, in operation, high loads on sections of the frame can cause the frame to break or crack rather than flex. Metal frames are also relatively dense and can transmit vibrations from one point on the frame (e.g., under the engine or a front wheel assembly connected to the head tube) to other points on the frame (e.g., under the seat).
In light of these and other disadvantages (e.g., rust and corrosion) with conventional metal motorcycle frames, a need exists for a strong but lightweight motorcycle frame which has few joints, a higher flex modulus, and reduced vibrational transmission. The subject matter disclosed herein meets these and other needs.